Method of manufacturing a thermally responsive switch



1955 E. o. ANDERSEN 3,224,075

METHOD OF MANUFACTURING A THERMALLY RESPONSIVE SWITCH 2 Sheets-Sheet 1 Original Filed Dec. 28. 1960 Hg. .2. Ag. 3.

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Altar/78 Dec. 21, 1965 E. o. ANDERSEN 2 Sheets-Sheet 2 Original Filed Dec. 28, 1960 321mg m; m w w mw g I 8 1.: r I l 5 5 3 3 m a u w 3% Attorney- United States Patent 3,224,075 METHOD 0F MANUFACTURING A THERMALLY RESPONSIVE SWITCH Edward 0. Andersen, Rock Falls, Ill., assignor to General Electric Company, a corporation of New York Original application Dec. 28, 1960, Ser. No. 78,922, now Patent No. 3,134,002, dated May 19, 1964. Divided and this application Nov. 1, 1963, Ser. No. 320,902

1 Claim. (Cl. 29155.5)

The present invention relates in general to thermally responsive switches, and more particularly to a method of manufacturing and calibrating thermally operated switches having snap action of the switch contacts. This application is a division of my original application Serial No. 78,922, filed December 28, 1960, now Patent 3,134,002.

Thermally operated switches having snap action of the switch contacts are frequently used to provide thermal protection for electric motors. In order to provide an efiicient protective switch for an electric motor, it is often advantageous to mount such a switch in a relatively small area, such as directly within or between the windings of the motor, so that the switch will respond directly to the ambient temperature of the windings. For such an application, it is, therefore, desirable to use a thermally operated switch that is very small in size. In these applications, the diminutive size of the switch has often made it considerably diflicult to adjust or see the desired snap action for the switch contacts and thereby calibrate the switch. It has, therefore, been found desirable to provide an improved thermally responsive switch which includes a simplified adjustment means for setting or calibrating the snap action of the switch contacts during the manufacture of the switch.

Accordingly, it is a primary object of this invention to provide an improved method of manufacturing and calibrating a thermally responsive switch having a simplified adjustment means.

Another object of my invention is to provide an improved method for manufacturing a thermally responsive switch wherein a resilient snap acting means is used in conjunction with the switch contacts.

In carrying out my invention in one form, I provide an improved method of manufacturing and calibrating a thermally responsive switch having an elongated housing and a pair of contacts disposed therein. A switch operating member is positioned within the housing and movable between two positions by a thermally responsive means to actuate the switch contacts. The operating member is continuously biased toward one of its positions by a toggle spring means to provide snap action for the switch contacts. A flexible elongated member engages the spring means and is stretched in tension outwardly of the housing for setting the biasing force supplied by the spring to the operating member. By varying the tension of the flexible member, the temperature differential between the opposite movements of the operating member may thereby be efliciently established. This switch construction forms the subject matter of and is claimed in my original co-pending application previously mentioned.

By my invention I first place the various switch elements of the thermally operated switch just described within the housing with the flexible elongated member engaging the toggle spring means and also protruding outwardly from the housing. The flexible member is then tensioned to vary the biasing force applied to the operating member by the snap acting spring means. After the desired biasing force for the switch has been set, the flexible member is then fastened to the housing to maintain the desired biasing force characteristic during the operation of the switch.

3,224,075 Patented Dec. 21, 1965 Further aspects of my invention will become apparent hereinafter, and the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention. The invention, however, as to organization and method of utilization, together with further objects and advantages thereof, may best be understood by reference to the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of an improved thermally responsive switch embodying my invention in one form thereof, with a pair of leads connected to the switch terminals;

FIG. 2 is a sectional side view of the switch of FIG. 1, with the insulating sleeve removed and the contacts in their normally closed position;

FIG. 3 is a sectional view taken along the lines 3-3 as indicated in FIG. 2;

FIG. 4 is a sectional end view taken along the lines 44 as indicated in FIG. 2, with the switch contacts in their closed position;

FIG. 5 is a view similar to the view of FIG. 4, but showing the switch contacts in their open position;

FIG. 6 is an exploded view showing the structural details of the various elements of the switch of FIG. 2; and

FIG. 7 is a sectional side view of a switch embodying my invention in alternate form thereof.

Referring now to the drawings and more particularly to FIGS. 13, I have shown a thermally responsive switch 1 wherein my invention has been advantageously employed. Certain structural features of this switch, other than those claimed in my co-pending original application referred to above, are the invention of Charles Grimshaw, and are described in detail and claimed in the co-pending application of said Grimshaw, Serial Number 78,923, filed December 28, 1960, now Patent 3,123,697 and assigned to the same assignee as the present invention. To furnish a diminutive housing for the various components of this switch, which also efliciently serves as a thermally responsive element, the tubular casing 3 has been provided. In the illustrated embodiment, the size of casing 3 approximates that of a cylindrical pencil having a length of less than two and one quarter inches. Contact terminal assembly 5 is welded to upper end 7 of the casing 3 and nut 9 is welded to the lower end 11 thereof (as viewed in FIG. 2) to provide a smooth and compact hermetically sealed housing for the various internal switch parts. To electrically insulate the housing and enable the switch to be readily inserted in the winding of an electric motor, as shown in FIG. 1, a sleeve 13 of suitable electric insulating material, such as Mylar, is formed around the housing. It will be understood that the sleeve 13 is thermally conductive and very thin, therefore having little resistance to the transfer of heat to the siwtch housing.

Turning now to a further discussion of the housing for switch 1, casing 3 is preferably made from a metallic material having a relatively high co-efiicient of expansion, such as stainless steel or brass. Contact terminal assembly 5 includes a cylindrically shaped terminal 15 which has an annular flange 17 formed at its inner end. End 7 of easing 3 is bent inwardly against the shoulder 16 of annular flange 17 and welded thereto to first close end 7 of the switch housing. Fixer contact terminal 19 extends axially through terminal 15, being separated therefrom and supported therein by fused electrical insulating material 21. Inner end 23 of the fixed contact terminal is flattened on opposite longitudinal sides (as shown in FIG. 2) to support fixed contact button 25 of the switch.

To close the other end 11 of casing 3, after contact terminal assembly 5 has been welded to casing 3, the various parts of the switch have been positioned within the housing, and the switch has been properly assembled, nut 9 is welded to the casing, preferably by spot welding, to hermetically seal the switch. As shown in FIG. 6, nut 9 includes a partially ring-shaped shoulder 26 which engages the major portion of end 11 of the casing 3. To further describe nut 9, it is partially cylindrical in configuration to seat against the inner Wall of casing 3, but is truncated or reduced to provide a flat side 9a parallel to the axis of the nut. In general, nut 9 thus has a D- shaped configuration. Flat side 9a of the nut allows flexible strip 27 to be extended outwardly from bottom end 11 of the casing after the assembly of the various parts within the housing, for the adjustment of the temperature differential before end 11 is sealed. The structure and function of the flexible strip 27 will be described in detail hereinafter and it constitutes an important aspect of my invention. The nut 9 also has a centrally disposed threaded aperture extending axially therethrough. This aperture is engaged by adjustment screw 29. The adjustment screw 29 serves to help calibrate the switch for proper response to the thermally responsive actuating forces, as shall hereinafter become apparent.

Turning now to a consideration of the interior of switch 1, as shown in FIGS. 2 and 3 (the separate parts being best seen in FIG. 6), an elongated support 35 is positioned longitudinally within switch cavity 37. This support 35 serves as a second thermally responsive element, is encased within the housing, and is preferably constructed of steel. More particularly, support 35 resembles in overall appearance, a generally U-shaped channel, and, as shown in FIG. 6, includes elongated sides 38 which are spaced apart in parallel relationship by longitudinally spaced U-shaped bight sections or ribs 39, 41, 43, 45, and 47. Stepped upper ends 49 of the sides 38 compressively engage the inner surface of terminal 15 on opposite sides of the inner end of fixed contact terminal 19. (See FIGS. 2 and 3.) Rib 39 is formed at the other end of support 35. As shown in FIG. 6, rib 39 includes an extension which is curved slightly inwardly or in the direction of sides 38 and has a sharp transverse knife edge 51 formed thereon. The purpose of the knife edge 51 is to transmit thermally responsive force variations from within the switch housing to a motion amplifying lever assembly, as shall become apparent hereinafter.

For pivotally supporting a switch actuating means, connecting rib 41 of support 35 is spaced longitudinally from end rib 39 by a slot 52. A pair of fingers 53 are spaced apart laterally and curved angularly inwardly from the inner surface of the upper end of rib 41 (FIG. 2). Fingers 53 extend angularly toward the left side of casing 3 and upwardly away from slot 52, as viewed in FIG. 2, having a space 54 therebetween (FIG. 6) and sharp outer edges which provide a pair of knife edge supports for switch actuator or operating member 55.

Switch actuator 55 resembles in general a U-shaped channel which is not as deep as support 35, as shown in FIG. 4. The structure of actuator 55, as best shown in FIG. 6, includes a pair of elongated sides 57 which are held together in parallel relationship by bight sections 65, 66, and 68. These bight sections are U-shaped and they are spaced apart longitudinally by the slots 59 and 61. Elongated bight section 65 extends between slot 59 and the bottom end 63 of the actuator. Section 65 has formed therein a centrally disposed lanced tab 67 and an adjacent stamped embossment 69. The free end of tab 67 extends angularly upwardly and to the right (viewing FIG. 2). Embossment 69 has the configuration of a D-shaped plateau on the right side thereof (FIG. 2). The bottom side of this plateau provides a pair of spaced apart transverse shoulders 71 (FIG. 6) which face toward end 63 of the actuator and are spaced slightly lon gitudinally upwardly from the free end of the tab 67 (FIG. 2). Shoulders 71 provide sharp inner edges which are transversely and linearly arranged.

Actuator 55 is positioned on the left side of the ribs of support 35 (viewing FIG. 2) with knife edges 53 of the support each linearly engaging beneath and against an associated one of the actuator shoulders 71. (See also FIG. 6.) The free end of lanced tab 67 projects angularly to the right, as shown in FIG. 2, and traverses between the knife edges 53 to laterally position the shoulders 71 upon their associated knife edges 53. The engagement of actuator shoulders 71 with knife edges 53 of the support thus provides an accuratepivotal support for the actuator with substantially minimal lateral movement of the actuator on its supporting pivots.

When actuator 55 is pivotally mounted upon support 35, L-shaped tab 72 of the support extends transversely to the left (FIG. 2) through slot 59 of the actuator and then upwardly, parallel to rib 43. The free end of tab 72 is thus positioned to the left of the bottom end of actuator bight section 66 (FIG. 2) to limit pivotal movement of the actuator in a counterclockwise direction or rotation.

To properly balance actuator 55 upon its pivots, a weight 73 of suitable magnitude is welded to the right side of bight section 65, as viewed in FIG. 2. In order to provide clearance for pivotal movement of the actuator 55 near bottom end 63 thereof, weight 73 lies generally within slot 52 of the support.

To operate the contacts of switch 1, and thereby control an external circuit, the upper end of actuator 55 (as shown in FIG. 2) is specially formed to pivotally support and carry movable contact strip 75. (See also FIG. 6.) More particularly, bight section 68 of actuator 55 has an embossed spring seat 79 formed thereon which projects to the left, as shown in FIG. 2. An L-shaped extension 81 is formed on an upper prolongation of section 68. This extension 81 includes transverse portion 83 and a switch actuating arm 85 which extends longitudinally within cavity 37 on the left side of fixed contact button 25 (FIG. 2).

To efficiently guide and pivot movable contact strip upon actuator 55, the strip 75 includes a channelshaped section 87 and a channel-shaped contact extension 89. Strip 75 is preferably formed from a thin strip of silver metal. The longitudinal axes of section 87 and extension 89 of the strip are generally perpendicular to each other. Opposed sides 91 and 93 of extension 89 are parallel to each other and spaced apart to allow a suitable wipe distance for movement of the free end 95 of the actuator therebetween. The sides of channel section 87 serve to position the movable contact strip laterally relative to the actuator, as shown in FIG. 3.

Movable contact strip 75 is positioned upon the L- shaped extension of the actuator 55, as shown in FIG. 2, with transverse portion 83 of the actuator extending through slot 94 of the contact strip. Free end 95 of arm of the actuator is then disposed to the left of extension side 93 between it and side 91. Movable contact button 97 is embossed on the right side of contact extension 8 9 and disposed opposite to fixed contact button 25.

To normally bias movable contact button 97 toward fixed contact button 25 and provide a wiping action, as will be hereinafter explained, embossed spring seat 99 is formed in the bight portion of channel section 87. Seat 99 is positioned so as to face seat 79 of the actuator. (See FIG. 2.) Spring 191 runs in compression between the oppositely disposed seats 79 and 99 of the actuator and movable contact strip, respectively, to normally urge movable contact button 97 in a clockwise direction of rotation (viewing FIG. 2), the strip 75 pivoting at slot 94 around transverse actuator portion 83. When the switch contacts are closed, end of actuator 55 is in engagement with side 93 of the movable contact strip 75. Spring 101 is then held in compression, as shown in FIG. 2, by the sandwiching of side 93 and the movable contact button 97 between actuator end 95 and rigid fixed contact 25.

Turning now to the provision in switch 1 of an adjustment means for setting or calibrating the biasing force applied to operating member 55, as shown in FIG. 2, U-shaped toggle spring 103 has been provided. This spring is in continuous compression between pivot edge 105 of flexible strip 27, and transverse projecting edge 107 which is formed on an upper extension of actuator bight section 66. Edges 107 and 105 of the actuator 55 and strip 27, respectively, engage indented end portions of the toggle spring 103, as shown in FIG. 2, to effect the snap action of the actuator about its pivots 71. Spring 103 pivots about strip edge 105 and continuously biases actuator 55 in the direction of the open position of the switch contacts, or with a counterclockwise moment of biasing force about pivoting shoulders 71 of the actuator.

To facilitate the adjustment of the biasing force applied to the switch actuator 55 by the toggle spring 103, after the various parts of the diminutive switch 1 are assembled within tube 3, the aforementioned flexible strip 27 is stretched in tension between the support rib 47 and the bottom end of the casing 3, as shown in FIG. 2. As shown in FIG. 6, strip 27 is elongated, and at its upper end, it has an enlarged rectangular section 109, with a rectangular slot 111 formed therein. To attach strip 27 to the support, the end of the strip near which slot 111 is formed is extended outwardly, perpendicularly away from, and then back parallel to the principal surface of the strip to provide a generally hooked-shaped fold 113. Fold 113 is wrapped around rib 47 of the support, as generally shown in FIG. 2, before the assembly of the various switch parts within the housing.

More particularly, in assembling switch 1, I preferably utilize several sub assembly operations, followed by the main assembly procedure. A housing sub assembly is achieved by welding contact terminal assembly 5 to upper end 7 of tubular member 3 (FIG. 6). A support sub assembly is put together by wrapping fold 113 of strip 27 around support rib 47 (FIG. 2). An actuator sub assembly is provided by pivotally mounting movable contact 75 upon actuator 55, with spring 101 extending between spring seats 79 and 99. The actuator sub assembly and support sub assembly are assembled together outside of the housing by pivotally mounting the knife edges of the actuator upon those of the support. Toggle spring 103 is then positioned between knife edges 105 of strip 27 and 107 of actuator 55.

For the main assembly operation, the assemblage of the support sub assembly and actuator sub assembly is positioned in tubular member 3 with bottom end 115 of strip 27 extending outwardly from end 11 of the tubular member. Lever 119 (which shall be described in detail hereinafter) is then inserted into cavity 37 of the housing 3 with its knife edge 129 engaging edge 51 of support 35. The shim 131 (which shall also be described in detail hereinafter) is next positioned on lever 119, as shown in FIG. 2. Nut 9 with screw 29 engaged therewith is thereafter welded to bottom end 11 of member 3, but not yet sealed thereto.

Bottom end 115 of strip 27, with a tool aperture therein, thus extends out of the housing over the flat surface 9a of nut 9 and is pulled to vary the position of pivot edge 105 longitudinally and downwardly. This movement of pivot edge 105 provides the desired compression and biasing characteristic for spring 103. The bottom of the strip is then welded between the right side of nut 9 and the adjacent bottom end 11 of the casing (FIG. 2) to set the spring biasing force at the desired temperature differential for the switch. Rectangular slot 111 provides clearance for the movement of both of the free ends of the toggle spring 103. Intermediate the ends of the strip 27, an outwardly raised surface 117 is projected toward the wall of the casing to help position the strip 27 within the casing and guide the longitudinal movement of the strip.

After the switch differential has been adjusted, and screw 29 has been rotated for desired switch calibration, the switch is hermetically sealed.

It will thus be seen that the structure of and disposition of strip 27 allows convenient setting of the biasing force imparted to actuator 55 by toggle spring 103 after the assemblage of the switch parts Within cavity 37. In addition, this setting means readily lends itself to the calibration of the biasing force for the actuator of a diminutive switch which is hermetically sealed.

To operate the actuator and contacts of switch 1 by two thermally responsive members, as shown in FIG. 2, in the lower portion of switch cavity 37, there is positioned the force transmission lever 119. Considering first the structure of lever 119, as shown in FIG. 2, it includes a force receiving section 121, an elongated force transmission section 123 which extends perpendicularly upwardly from the left side of section 121, and an actuating section 125 which extends angularly from the upper end of section 123 toward the upper end of the recess formed by embossment 69 in the actuator 55. The outer side of force receiving section 121 has a V-shaped knife edge 127 projecting outwardly therefrom. This edge 127 is accurately formed so that it is perpendicular to the longitudinal center line of lever 119 (as may be seen in FIG. 3). On the opposite or inner side of force receiving section 121, and spaced between edge 127 and the adjacent right end of the lever (FIG. 2), the shallow V-shaped groove 129 is formed. The innermost extremity of this groove is accurately parallel to the knife edge 127 and also perpendicular to the longitudinal center line of the lever 119 (viewing FIG. 3).

Lever 119 is assembled within switch cavity 37 with the right-angled shim 131 overlying the adjacent outer surfaces of force receiving section 121 and section 123. The inner end of adjustment screw 29 has a frusto-conical shape and it engages the outer side of leg 132 of the shim. The inner side of the shim leg 132 is sharply engaged by knife edge 127 of force receiving section 121 to imbed a knife edged indentation therein. The engagement of knife edge 127 with shim leg 132 provides an accurate pivotal relationship between the housing of the switch and lever 119 which is precisely preserved during the rotation of screw 29 by the engagement of the legs of the shim with the adjustment outer surface of sections 121 and 123.

The transverse knife edge 51 of support 35 pivotally engages the shallow groove 129. Support 35 runs in compression between annular flange 17 at the upper end of cavity 37 and grooves 129 of lever section 121. It will thus be seen that force receiving section 121 of lever 119 is in compressive engagement with the switch housing by means of screw 29, shim 131, and the V-shaped knife edge 127, and it is also in compressive engagement with the support 35 by means of knife edge 51 and groove 129. The offset points 127 and 129 of the lever thus receive compressive forces from the housing and support, respectively. Each of these compresssive forces urges the free end of actuating section 125 of the lever to rotate in a clockwise direction of rotation, as shown in FIG. 2, about the pivot which is compressed by the other force. For example, the compressive arrangement of support 35 within the switch cavity 37 imparts a compressive force to groove 129 of the lever. This compressive force urges the free end of actuating section 125 to rotate in a clockwise direction of rotation about knife edge 127. The compressive force imparted to knife edge 127 by screw 29 through the shim 131 urges the free end of actuating section 125 of the lever to rotate in a clockwise direction about pivot point 129. The particular construction of lever 119 and its engagement with the housing, the support and the actuator 55 comprises the invention of Charles Grimshaw, and this construction and arrangement are described and claimed in his aforesaid co-pending application Serial Number 78,923, now Patent No. 3,123,697.

Turning now to a detailed description of the operation of thermally responsive switch 1, as shown in FIG. 2, movable contact button 97 is in its normally closed position, in engagement with fixed contact button 25. With the contacts of the switch in their normally closed position, the compressive forces imparted to lever 119 at pivots 127 and 129 by the housing and the support are of sufficient magnitude to hold actuator 55 in its closed position against the biasing force of toggle spring 103. With the switch contacts in this position, a major electric current path is provided through the switch from the cylindrically-shaped terminal 15 to the fixed contact terminal 19, through the support 35, the actuator 55, the movable contact strip 75, and the fixed contact button 25. The other conductive parts of the switch, such as the casing and lever form parallel paths to a portion of the major path, but whatever path is considered, the contacts 97 and 25 will open it when they are separated.

Let us suppose that switch 1 is connected to the control circuit of an apparatus, such as a hermetically sealed motor and supported at upper end 7 of casing 3. The housing of the switch is electrically insulated from. its external supporting environment by the aforementioned sleeve 13. When a relatively high rate of ambient temperature occurs, the tubular casing 3 senses this rapid temperature variation considerably faster than the support 35, due to the shielding effect the housing has upon the support. The thermal expansion or contraction of the support 35 always lags that of the tubular member 3 for an increase or decrease in temperature.

With a relatively high rate of increase in ambient temperature, the bottom end 11 of the tubular casing 3 expands longitudinally downwardly a few ten thousands of an inch from where it is shown in FIG. 2. Nut 9 and screw 29 also move downwardly with casing 3, since they are attached thereto, and the compressive force imparted to knife edge 127 of lever 119 via shim 131 is thereby rapidly reduced. With a rapid reduction in compressive force at knife edge 127, actuating section 125 of lever 119 is ultimately (i.e., at the value of the predetermined ultimate strip temperature) allowed to move in a counterclockwise direction of rotation (viewing FIG. 2) by the counterclockwise biasing force exerted thereupon by the spring biased actuator 55. This motion causes actuator 55 to move in a counterclockwise direction of rotation about its pivots. The biasing force of toggle spring 103 moves the free end 95 of the actuator away from inner side 93 of the movable contact extension (where it is shown in FIG. 2) toward outer side 91 thereof. As the free end of the actuator begins to move away from side 93 toward side 91, the compressive force applied by spring 101 to the movable contact strip urges the movable contact button to rotate in a clockwise direction. Spring 101 thus retains the contacts in engagement until the free end 95 of the actuator has traveled the wipe distance (i.e., the approximate distance between the inner surfaces of sides 91 and 93 minus the thickness of the actuator at its free end 95). The free end 95 of the actuator then engages side 91 of the movable contact strip and thereby pivots the movable contact button 97 out of engagement with the fixed contact button 25. This is the open contacts position for the switch.

After the switch contacts have been opened, when the tubular member 3 is cooled, it contracts and thereby diminishes in length. With the occurrence of this temperature condition, lever 119 eventually receives a sutficient compressive force at pivot 127 from the switch housing to overcome the spring biased actuator and reclose the contacts.

Supposing now that switch 1 is exposed to a relatively low rate of increase in temperature, when this ambient condition occurs, the tubular casing 3 and support 35 each expand longitudinally in the same direction, downwardly as shown in FIG. 2, or away from the contact end of the housing. The containment of of support 35 by the switch housing has less effect upon transfer of heat to the support for this condition and support 35 receives a significant effect from the thermal variation. Tubular casing 3 thus expands longitudinally a few ten thousands of an inch, with support 35 expanding longitudinally in the same direction, but to a lesser degree. The compressive force exerted upon knife edge 127 of the lever by screw 29 is then reduced by the thermal expansion of casing 3, but at the same time, the compressive force urged upon pivot groove 129 of the lever by support 35 is gradually increased by the thermal expansion of the support. It will thus be seen that the thermal expansion of support 35 partially compensates for the thermal expansion of tubular casing 3 when the rate of rise in temperature is low enough to allow significant transfer of heat into cavity 37 of the casing. Since the thermally responsive compressive force urged upon lever 119 by support 35 increases in response to temperature rise and partially compensates for the diminishing of the compressive force exerted upon the lever by the housing, when there is a relatively slow temperature rise in lieu of a relatively rapid temperature rise, it is necessary for the ambient temperature to reach a higher predetermined value before the contacts of the switch will open. When this higher predetermined temperature value has been reached, actuator of the switch will open the contacts in the same manner as previously described for the relatively high rate of temperature variation.

It will now, therefore, be seen that I have provided a new and improved method of manufacturing a thermally responsive switch having a very simplified and eificient means for setting the spring biasing of the switch operating member. This setting means may be assembled in the switch by my improved and expeditious method which readily lends itself to mass production manufacturing techniques. Thus, in accordance with my invention, a very diminutive switch may be easily calibrated during the manufacturing operation thereof.

FIG. 7 illustrates a modified form of thermally responsive switch 1, the modified form being generally indicated by numeral 140. For switch 140, the same reference numerals have been employed to indicate switch parts that have heretofore been described for switch 1. Parts which have a modified structure in comparison to the structure of their correlative parts in switch 1 but perform the same basic functions in the switch are identified by the same reference numeral with the letter a suffixed thereto.

To eliminate some of the manufacturing tolerances which would occur in making the switch, support 35a has an upper end rib 142 (as shown in FIG. 7) with tab portion 141 formed thereon. Tab portion 141 extends angularly downwardly and away from the bottom side of rib 142 toward the adjacent inner wall of casing 3. The free end of tab portion 141 abuts the casing wall to force the upper end of support 35a laterally toward the left side of the casing (viewing FIG. 7) and thereby reduce the building up of tolerances during the manufacturing operation for the switch 140. To facilitate clearance for the right side of fixed contact button 25 (FIG. 7), when the upper end of support 35a is positioned in the cavity of switch 140 by tab portion 141, aperture 143 is formed directly to the right of contact button 25.

In order to hermetically seal the bottom end of switch 140, it will be noted that nut 144 thereof is smaller than nut 9 of switch 1 and is fitted inside of casing 3 near its bottom. Nut 144 has the same D-shaped configuration as nut 9, but the cylindrical peripheral portion thereof is smooth. A special flat protuberance 147 is formed on the fiat right side of nut 144 (FIG. 7). Nut 144 is welded to the inner wall of the casing 3 at 145. Protuberance 147 extends longitudinally in a plane parallel to the axis of screw 29, and it serves as a supporting pro ection for receiving the weld of flexible strip 27a after the temperature differential has been properly set. Free end 149 of flexible strip 27a is then looped transversely within the bottom of the cavity, as shown in FIG.

7, outwardly of screw 29. After screw 29 is properly adjusted to calibrate the compressive forces exerted upon lever 119, it is Welded to nut 144 at 146. Cup-shaped cap 151 is then pressed into its position, as shown in FIG. 7. Cap 151 is flush with the edge of the tube and the smooth surface of its annular rim 153 engages the inner wall of the casing near its bottom. The cap 151 is then welded to the casing, preferably by the heli-arc method, to hermetically seal the switch 140.

operationally, thermally responsive switch 140 is identical to the arrangement of switch 1 which has been previously described.

While in accordance with the patent statutes, I have described what at present are considered to be the preferred embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and I, therefore, aim in the following claim to cover all such equivalent variations as fall Within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A method of manufacturing 'a thermally responsive switch wherein a U-shaped toggle spring has two oppositely disposed indented portions and continuously biases an operating member toward one of two switch positions within a hermetically sealed elongated housing, said method comprising the steps of Wrapping one end of an elongated flexible strip around the transverse rib of a support; pivotally mounting the operating member upon said support; placing one indented portion of the U-shaped toggle spring in pivotal engagement with said strip and 10 placing the other indented portion of the toggle spring in biasing engagement with the operating member; inserting the switch elements including the support, the strip attached thereto, the toggle spring, and the operating member within said housing through one end thereof With the other end of the elongated strip extending outwardly from said housing end, one end of the housing, providing an abutment for the support at said one end, tensioning said flexible strip to move the associated indented portion longitudinally toward said abutment of said one end of the housing and thereby vary the biasing force applied to said operating member by the toggle spring; fastening said flexible strip to said housing to maintain the desired biasing force characteristic during operation of said switch, and hermetically sealing said housing.

References Cited by the Examiner UNITED STATES PATENTS 1,976,843 10/1934 Eskin ZOO-'67 XR 1,977,393 10/1934 McCormick 200-67 2,611,845 9/ 1952 Miller 200-67 XR 2,698,880 1/1955 Sandberg 20067 XR 2,877,539 3/1959 Kinnan 29-155.5 2,892,050 6/ 1959 Fisher 200-67 XR 2,992,288 7/1961 Betz 200137.2 3,032,628 5/1962 Elwood 200-87 JOHN F. CAMPBELL, Primary Examiner.

WHITMORE A. WILTZ, Examiner.

R. W. CHURCH, Assistant Examiner. 

